Two related copper-containing monooxygenases, peptidylglycine ?-amidating monooxygenase (PHM) and dopamine-_-hydroxylase (DBH), are of particular neurological importance, since they catalyze final steps in the biosynthetic pathways leading to messenger molecules such as amidated peptides and catecholamine neurotransmitters. This proposal is focused on investigating the catalytic role of copper, and the relationship between structure and function in this important class of copper monooxygenase. We will use x-ray absorption spectroscopy to probe the structure of the wild-type forms of PHM, together with selected mutants, with the goal of answering questions related to (a) the role of the methionine ligand coordinated to Cu(I) at the dioxygen binding site; (b) the involvment of protein-based radicals involved in the catalytic mechanism; (c) the structures of putative reduced oxygen catalytic intermediates; and (d) the role of CuA in intramolecular electron transfer.